MATTHEW HERPER IN FORBES - WHAT IF MIKE BLOOMBERG IS RIGHT AND A CLIMATE CHANGE NIGHTMARE IS HERE?

Monday night, denial was a river in Manhattan. It was affecting me. I had almost flown out-of-state, away from my wife and two young children. It was affecting my friend, the best-selling author and journalist Alex Berenson, who at 2:37 pm tweeted: “#Sandy tip: When the forecasters tell you the storm’s category doesn’t matter because it’s just so big, turn your TV off.” It was affecting the billionaire Kenneth Langone, who, according to a Bloomberg News report, was being treated for pneumonia in his namesake hospital on the east side of Manhattan. Who could believe that the kind of superstorm predicted by weather forecasters and climate scientists was actually about to hit?

By the time the winds hit my waterfront Brooklyn neighborhood, as a facade ripped off a building across the street and pictures poured in of apartments in Red Hook, a mile south, filled with brackish water, I couldn’t imagine that I might have been in another state. A power station at 14th Street and Avenue C went up in a blue flash, and Alex tweeted: “All right, this is a genuine mess.” Langone went home, because New York University Langone Medical Center had to be evacuated as its backup generators failed. The doctors and nurses at his hospital, working heroically, moved 215 patients, including infants on ventilators whose lungs were kept working with hand-operated plastic bags, to other hospitals like Mount Sinai Medical Center four miles north. On Tuesday, I spoke to Kenneth Davis, Mount Sinai’s president. He told me that he was getting more calls from east side hospitals battered by the surge. Bellevue Medical Center, our biggest public hospital, has also been evacuated, and NYU’s Hospital for Joint Diseases ten blocks south had stopped accepting new patients.

Lower Manhattan was almost entirely without power, probably until tomorrow. Staten Island was devastated. At least 38 New Yorkers are dead. The devastation in the nearby Jersey Shore is even worse. Nobody knows when the subway system will be running between Manhattan and other boroughs again. It’s true, as ProPublica pointed out, that the hospital evacuations are part of an epidemic of hospital generators failing during natural disasters, and that the generators were, in the words of NYU Langone trustee Gary Cohn, “not state-of-the art and not in the most state-of-the art location.” We couldn’t come to emotional terms with the destruction a fourteen foot wall of water could do to this city. Now we don’t have any choice.

“In just 14 months, two hurricanes have forced us to evacuate neighborhoods — something our city government had never done before. If this is a trend, it is simply not sustainable,” wrote New York Mayor Michael Bloomberg in his endorsement of President Barack Obama. “Our climate is changing. And while the increase in extreme weather we have experienced in New York City and around the world may or may not be the result of it, the risk that it might be — given this week’s devastation — should compel all elected leaders to take immediate action.”

I’d like to say it was unimaginable, but it had been imagined. This video, recorded by Wall Street Journal Science columnist Robert Le Hotz a year ago, lays out very much what happened to this city. It was imaginable. It just wasn’t believable. Now many of us, in the wake of a storm that weather scientists got very much right, should face the fact that this particular brand of extreme weather may be very much a trend. Because scientists who study climate agree that it is being modified by the human release of greenhouse gasses like carbon dioxide and methane and that this puts places like New York City at risk.

The view that the world’s climate is being warmed by human behavior is accepted by every major scientific organization. What is still up for debate is whether those effects are big enough to result in more strong storms hitting the Northeast (see this post by Andrew Revkin at the New York Times or this one, by the Houston Chronicle’s Eric Berger.) And some scientists believe very strongly that it is.

“While one storm ‘might have happened anyway’ in a mythical non-industrial world, the general level of weird weather (an amalgam of many events) is clearly caused by anthropogenic greenhouse gases,” says David Archer, a professor at the University of Chicago, in an email. “Like you could figure out that dice are loaded by tossing them a few times, more than just once.” (His book, The Long Thaw, is one of the best quick reads on climate change.)

But even if you don’t buy the argument that the weather has gotten totally weird, there is a less controversial reason to blame global warming for the flooding of New York: the fact that the sea is rising. That is both because ice is melting and because the water is warming, causing it to expand. The higher the sea level, the more likely there is to be a surge.

“Surge risk is tangibly affected by sea level rise, so that a mere 1-foot rise in mean sea level might double the rate of occurrence of strong storm surges,” writes Kerry Emanuel, a climate researcher at the Massachusetts Institute of Technology. “Also, as the atmosphere warms, it can hold more water so that, almost certainly, hurricanes will rain more as the climate warms. This will increase the incidence of hurricane-produced flooding.

“There is a great deal of evidence that the warming of the oceans over the last 30 years or so is owing to increasing greenhouse gas concentrations,” Emanuel continues. “The theory, models, and observations all line up. We know the exact rate at which seawater expands with temperature, and the expected increase in sea level calculated from the observed increase in temperature matches the observed rate of increase of sea level.”

Forty million years ago, when the earth was warmer because there was more carbon dioxide in the air as a result of volcanic eruptions, the oceans are thought to have been 70 meters (or 229 feet) higher. Stefan Rahmsdorf, a professor of oceanography at Potsdam University in Germany, says that sea levels were basically flat for most of the past 2000 years, but in the past 100 have increased faster than ever before. The idea that sea levels are rising quickly now is not controversial, and was seen as a pretty firm conclusion by the Intergovernmental Panel on Climate Change back in 2007.

Rahmsdorf points to a paper written by colleagues of his that used measures of how sediments build up in salt marshes in North Carolina and surveys of what type of microscopic shells could be found in them. Average sediment buildup, measured in a core of mud, follows the sea level, but not exactly; but the height of the water also changes what microscopic sea life live there. Measuring both gives a good estimate of how high the water was at that time. You can find a more full explanation of that study here.

Does all this mean that Sandy was the one-and-only cause of what happened in New York? No. Storms happen. A Category 4 storm in 1821 created a 13-foot storm surge; and 1815 storm separated Long Beach and the Rockaways on Long Island. A 1938 hurricane hit the surrounding areas hard, though let New York City off easy. You can argue that, statistically speaking, NYC was due. But if the situation is getting worse, there may be other steps that should be taken aside from just cutting greenhouse gas use. Henry Blodget and Slate’s Matthew Iglesias both just suggested building a multi-billion dollar flood barrier around the city.

It’s hard for me to be objective about this. If I was raised with any guiding philosophy, it was that one should listen to scientists. And I’m very much a New Yorker. On Tuesday, after the storm had passed, I gave my family the slip and walked a mile south through Red Hook, first past houses and businesses that were still bilge-ing out waist-deep water on Van Brunt Street, than over to Lorraine Street, where I heard the water had been high that morning, and the Red Hook Houses, a housing project. It was gray and dark, with no electricity in the tall towers, and people either ambling numbly on the street or marching to and from darkened apartments. “This is a nightmare!” one woman shouted to another woman, a friend. The friend put an arm around her and replied, “It’s a nightmare that’s already happened.” This too shall pass, she seemed to be saying. The science of climate change may be murkier than my colleagues at Bloomberg Business Week, who proclaimed “It’s Global Warming, Stupid,” might like. But I hope that that this is a nightmare that happened, not one that is beginning.